Dental restorations represent one of the conceptually simplest biomaterials - essentially requiring the restoration of mechanical function in an aesthetically acceptable manner. Yet, despite that conceptual simplicity, an array of complex and often conflicting material, biological, curing and reaction properties necessitate a series of suboptimal solutions. Hundreds of millions of restorations are performed each year and premature failure of these restorations results in the need for a far greater number of restorations, including the occasional removal of additional healthy tooth structure. The need for simple, biocompatible, easily manipulated aesthetic dental restoratives has pushed the community towards polymeric composites that are readily reacted in situ, generally by photoinitiation, to yield a high modulus, high strength composite structure that is tooth-like in appearance. Despite the importance of these materials, the resin (i.e., the polymerizable component) phase of these systems has remained largely unchanged since its introduction several decades ago. The common use of dimethacrylate-based resins for dental restorative materials is plagued by critical problems; they do not achieve complete conversion of the methacrylates and thus leave a great deal of material that can be extracted into the oral environment. Further, these materials are prone to significant shrinkage and shrinkage stress that arises during the polymerization/curing process that is used to set the material. Thus, here, we propose a revolutionary new approach to dental materials based on the nucleophile- catalyzed thiol-vinyl sulfone network forming reaction. The proposed thiol-vinyl sulfone dental composite system will significantly improve upon the biological, chemical reaction and mechanical behavior of traditional methcrylate based composite systems. Based on exciting preliminary results that demonstrate the ability to achieve complete functional group conversion via this highly efficient, rapid reaction; appropriate mechanical behavior from the polymers formed; low shrinkage and stress; and the elimination of enzymatically reactive functional groups from the resin, we hypothesize that resins formed by this thiol-vinyl sulfone reaction represent ideal candidates as dental restorative materials. The overall aim is to develop and evaluate dental composites based on the nucleophile catalyzed thiol-vinyl sulfone Michael addition reaction that will include the development of appropriate monomers and functionalized fillers, the development of highly reactive photoinitiator systems for these resins, and the demonstration of acceptable fatigue, extractables, biocompatibility, degradation and other essential short- and long-term composite behavior. Ultimately, the overall aim is to establish these thiol-vinyl sulfone-based composites as a disruptive change in the dental composite field. We will demonstrate over the course of this grant period that these materials are capable of achieving more than a two-fold increase in service lifetime based on dramatically reduced extractables, swelling, degradation and wear in longterm, environmentally challenging testing conditions.